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Detection of an atmosphere on a trans-Neptunian object beyond Pluto

Nature Astronomy volume 10, pages 980–987 (2026) Cite this article

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Abstract

The only trans-Neptunioan object (TNO) with a detected atmosphere so far is Pluto, which has an average surface pressure of 10 μbar. Investigations of other large (>500 km) TNOs have only been able to establish upper limits of 1–100 nbar. A recent near-infrared study reported methane gas emission from Makemake, although its origin remains uncertain. Here we report that a stellar occultation campaign performed on 10 January 2024 of the ~250-km-radius plutino (612533) 2002 XV93 reveals a refractive signature, indicating a thin atmosphere. We derive a surface pressure of 100–200 nbar, above the previous limits for other larger bodies. This discovery shows that even a few-hundred-kilometre TNO can host, at least transiently, an atmosphere, challenging standard volatile-retention scenarios. Our findings suggest that a fraction of distant icy minor planets can exhibit atmospheres, potentially sustained by ongoing cryovolcanic activity or produced by a recent impact of a small icy object.

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Fig. 1: Sky-plane projection of the 2002 XV93 stellar occultation detections.
Fig. 2: Light curves of the possible atmospheric features.
Fig. 3: 2002 XV93’s atmospheric refraction profile.
Fig. 4: Atmospheric pressure constraints on TNOs.

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Data availability

The observational data used in this study, and the photometry and model refraction profile data underlying the figures, are available via Zenodo at https://doi.org/10.5281/zenodo.18976431 (ref. 53).

Code availability

The SORA software packages46 was used to predict the occultation event and analyse the data presented in this Article. Codes written for this study are available from the corresponding author upon request.

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Acknowledgements

This research has been partly supported by Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) grant nos. 18K13606 and 21H0115.This research is partially supported by the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) programme funded by the MEXT of Japan. The TABASCO campaign is partially supported by the International Occultation Timing Association – East Asia (IOTA/EA).

Author information

Authors and Affiliations

  1. National Astronomical Observatory of Japan, Mitaka, Japan

    Ko Arimatsu & Jun-ichi Watanabe

  2. Ishigakijima Astronomical Observatory, National Astronomical Observatory of Japan, Ishigaki, Japan

    Ko Arimatsu

  3. The Hakubi Center/Astronomical Observatory, Graduate School of Science, Kyoto University, Kyoto, Japan

    Ko Arimatsu

  4. University of Occupational and Environmental Health, Japan, Kitakyushu, Japan

    Fumi Yoshida & Takafumi Ootsubo

  5. Planetary Exploration Research Center, Chiba Institute of Technology, Narashino, Japan

    Fumi Yoshida

  6. Saga Hoshizora Astronomy Center, Saga, Japan

    Tsutomu Hayamizu

  7. Institute of Astronomy, Graduate School of Science, The University of Tokyo, Mitaka, Japan

    Satoshi Takita

  8. Japan Occultation Information Network, Miharu, Japan

    Katsumasa Hosoi

  9. Koyama Space Science Institute, Kyoto Sangyo University, Kyoto, Japan

    Jun-ichi Watanabe

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  1. Ko Arimatsu
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Contributions

K.A. planned and organized the campaign, made the occultation prediction, participated in the observations, obtained and analysed the data, and interpreted the data and wrote the paper. F.Y. helped organize the campaign, interpret the data and write the paper. T.H. helped to plan the campaign. S.T. participated in the observations, obtained and analysed the data, and helped write the paper. K.H. participated in the observations and obtained and analysed the data. T.O. and J.W. helped interpret the data and write the paper.

Corresponding author

Correspondence to Ko Arimatsu.

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Nature Astronomy thanks Ian Wong and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data

Extended Data Fig. 1 Prediction map of the 2002 XV93 stellar occultation event on 10 January 2024.

The red line shows the predicted central path of the occultation shadow, calculated using the JPL18 orbital elements and the Gaia DR3 stellar catalogue with the open-source package SORA46, and the blue solid lines correspond to the shadow width assuming a diameter for 2002 XV93 of 275 km. The blue dashed lines represent the 1σ error range. The red circle indicates the location of the positive detections (Kyoto and Kiso). The black point represents the Fukushima site, where the observed light curve shows no clear detection of an occultation by the main body but exhibits a possible gradual drop. Map data from Natural Earth, rendered via Cartopy within SORA.

Extended Data Fig. 2 Three-station light curves of 2002 XV93’s stellar occultation on 10 January 2024.

The flux points (points with error bars) observed at Kyoto (a), Kiso (b) and Fukushima (c) are overlaid with synthetic light curves (red lines, assuming a pure CH4 atmosphere and a best-fit surface pressure of 124 nanobars) as a function of time. In panel c, the grey points are the flux points for the individual exposures, and the black points are those binned by a factor of 8. The vertical arrow represents the closest-approach time to the shadow edge at Fukushima, at 13:12:50.818 UT. All error bars indicate 1σ (68%) uncertainties.

Extended Data Fig. 3 Atmospheric refraction profiles with different assumed bulk densities.

The same as Fig. 3, but overlaid with the synthetic refraction profile assuming the bulk density of 2002 XV93 to be ρ = 1.0 × 103 kg m−3 (dashed line). The three panels correspond to different assumed atmospheric composition cases (a, pure CH4; b, N2-dominant; c, CO-dominant). All error bars indicate 1σ (68%) uncertainties.

Extended Data Fig. 4 χ2 map for the light-curve fit.

The distribution of χ2 values as a function of the circular shadow radius R and surface pressure p obtained by the light-curve fit to the pure CH4 (a), N2-dominant (b), and CO-dominant (c) atmosphere-refraction model.

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Arimatsu, K., Yoshida, F., Hayamizu, T. et al. Detection of an atmosphere on a trans-Neptunian object beyond Pluto. Nat Astron 10, 980–987 (2026). https://doi.org/10.1038/s41550-026-02846-1

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